An elevator typically comprises an elevator car and a counterweight, which are vertically movable in a hoistway. These elevator units are interconnected to each other by a suspension roping that suspends them on opposite sides of a drive wheel. For providing force for moving the suspension roping, and thereby also for the elevator units, the elevator comprises a motor for rotating the drive wheel engaging the suspension roping. The motor is typically automatically controlled by an elevator control system.
The ropes on opposite sides of the drive wheel pass in the hoistway at a certain distance from each other (later referred to as rope-to-rope distance). In elevator design, the rope-to-rope distance cannot be freely chosen. Typically, the rope-to-rope distance is largely defined by the size and position of the movable elevator units, in particular car size and counterweight position in shaft layout. In prior art, one diverting wheel has been added in the system so as to attain more flexibility for the rope-to-rope distance. This kind of arrangement is illustrated in FIG. 1. In this case, on one side of the drive wheel, the rope has passed directly to one of the elevator units and on the other side around said diverting wheel. Thereby, the rope-to-rope distance has been possible to adjust suitable by adjusting lateral position of the diverting wheel.
In elevators, the roping comprises at least one but typically several ropes passing alongside each other. There are elevators where the ropes are belt-shaped, i.e. they have a cross section with width substantially greater than the thickness thereof. Position of the belt-shaped ropes relative to each wheel around which it passes (in the axial direction of the wheel) as well as relative to each other needs to be controlled so that adjacent ropes do not drift too close to each other, and so that none of the ropes drifts in said axial direction away from the circumferential surface area of the wheel against which the rope in question is intended to rest. One way to control this axial position of the belt-shaped ropes is to shape the circumferential surface areas of the wheel cambered. Each cambered circumferential surface area has a convex shape against the peak of which the rope rests. The cambered shape tends to keep the rope passing around it positioned resting against the peak thereof, thereby resisting displacement of the rope away from the point of the peak.
In prior art, a drawback has been that some configurations have been difficult to make utilizing cambered wheels. Particularly, when the rope-to-rope distance needs to be close to but a little wider than drive wheel diameter, the rope control in said axial direction has not worked reliably when utilizing cambered shape for rope position control. In these circumstances, the rope has been noted to be prone to wander in axial direction along the cambered shape. At worst, this behavior could cause the rope to move completely away from the cambered wheel. Therefore, it has been problematic to build a system utilizing cambered shape for rope position control where rope-to-rope distance is wider than but close to the diameter of the drive wheel.